1. Field of the Invention
This invention relates to polypropylene resin compositions having improved properties. More particularly, this invention relates to polypropylene resin compositions having far superior transparency, excellent anti-blocking property and good heat-sealability (ability to form heat-sealing), which is obtainable by compounding a hydrogenated resin of a thermally copolymerized resin of cyclopentadienes and aromatic hydrocarbons to polypropylene.
More specifically, the invention is to provide polypropylene resin compositions to which heat-sealability and anti-blocking property, which are not inherent in poly-propylene films, are provided without impairing the excellent mechanical characteristics which are inherent in polypropylene films, and yet in which an excellent transparent inherent in polypropylene films is further improved.
Polypropylene films possess extremely superior mechanical characteristics, impermeability to gases and moisture, transparency, and glossiness. Because the above-mentioned characteristics are similar to those of cellophane, polypropylene films have wide packing uses. However, there is a problem that they are inferior to cellophane with respect to heat-sealability and transparency.
2. Description of the Prior Art
Compounding natural resins, petroleum resins, or their hydrogenated materials has been proposed as a means for providing polypropylene film with sufficient properties for packing uses, e.g. heat-sealability and anti-blocking property (for example, Japanese Patent Publication Nos. Sho 52(1977)-39420 and Sho 57(1982)-36938). As the resins to be compounded to polypropylene, natural resins such as terpene-type resins and rosin-type resins, and aliphatic or aromatic-type petroleum resins are used, and especially hydrogenated products of these resins are highly appraised.
However, these resins to be compounded into polypropylene films still have disadvantages to be improved, and thus there are no resins which satisfy with a good balance of all the characteristics required of packing uses. For instance, natural resins are supplied only with uncertainty and are not constant in their quality. In addition, they are not economical. Aliphatic-type hydrogenated resins can provide superior transparency but low anti-blocking property. On the other hand, cyclopentadiene-type hydrogenated resins can provide excellent tensile strength, anti-blocking property and moisture-barrier-property, but in case of blending them with polypropylene they scarcely improve and even lower the transparency inherent in polypropylene films.